Is there a new method to calculate the enthalpy changes by DTA data?
I read this article, "Using DTA to quantitatively determine enthalpy change over a wide temperature range by the "mass-difference baseline method'' " which published in 1999 but I think the formula is a computational error.
Thanks
With modern DTA instruments you can get data almost as accurate as DSC if you are careful. Make sure your calibration sample volumes are similar (ideally you would want the exact same shape material too, although that is difficult because standard materials are typically foils, wires, or crystalline granules). For each standard you'll need to scan through the melting/freezing transitions 4 times, and ignore the first melt/freeze peaks. Average the peak area for the 3 remaining melt events (micro-volt seconds per gram). You know what the true enthalpy of melting is for your standard material (kJ/mol), so you now have calibrated your DTA signal at the melt temperature of that standard. Repeat the process over the entire range of interest and you can construct a calibration curve of micro-volt seconds per gram / kJ/mol against temperature.
I would perform a DSC analysis in order to obtain enthalpy values (below 600 C). The enthalpy is related to the inegrated area of event peak. DTA systems normally are not thermally isolated. Hope It helps you!
With modern DTA instruments you can get data almost as accurate as DSC if you are careful. Make sure your calibration sample volumes are similar (ideally you would want the exact same shape material too, although that is difficult because standard materials are typically foils, wires, or crystalline granules). For each standard you'll need to scan through the melting/freezing transitions 4 times, and ignore the first melt/freeze peaks. Average the peak area for the 3 remaining melt events (micro-volt seconds per gram). You know what the true enthalpy of melting is for your standard material (kJ/mol), so you now have calibrated your DTA signal at the melt temperature of that standard. Repeat the process over the entire range of interest and you can construct a calibration curve of micro-volt seconds per gram / kJ/mol against temperature.
The calibration method (as described by Eric for example) is crucial. The heating rate has to be optimized. The "shape" of the sample (powder, pellet, even the position in the crucible...) is important. The ambient gas may have an effect if the compound is sensitive (moisture, oxygen...); a closed crucible is advisable in some cases.
I suggest DSC measurements and calibration with a serie of compounds of knowing enthalpy.
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